Therapeutic intermittent compression of the limbs for the enhancement of blood circulation has been in use for the last couple of decades. A variety of conventional devices have been developed for the therapeutic intermittent compression of the limbs, with many being specifically developed for the prevention of deep vein thrombosis (“DVT”) after surgeries, others where developed and used for the treatment of arterial related problems such as peripheral vascular disease and diabetic ulcers. Thrombosis creation is effected by three major parameters, which are known as the Virchov's triad, namely: venous stasis, hypercoagulability state, initial damage to the tissues and/or the blood vessel wall.
Therapeutic intermittent compression of the leg, by pneumatically compressing the limb or using other mechanical compressive force upon the limb, uses the technique of cyclically compressing the limb so as to enhance circulation of blood. The compressive force exerted on the limb is mediated to the vein through the tissues causing it to constrict, thereby emptying the blood within it.
Improving the venous return is known to have a positive effect on the increase of the local arterial flow probably through the mechanism of increasing the Δp across the capillaries and through the increase in local synthesis of metabolites, prostacyclin (PGI2) and endothelial derived relaxing factor (NO). Both metabolites are synthesized by the endothelial cells as a response to the increase in shearing forces. The metabolites are considered the most potent native vasodilators available in the human body.
The period of compression is typically short (up to a few seconds) and the interval between pulses longer (more then 30 sec) which is the time it usually takes the veins to refill after being emptied by the relatively short pulse of compression.
The external compression methodology's favorable effect is derived from its ability to increase the peak venous velocity, thereby combating the stasis factor. The short period of increased linear venous flow velocity has also been demonstrated to significantly enhance blood clearance from the soleal sinuses, the axial veins, and the valve sinuses. Moreover, it has been shown that the cyclic increase in peak venous velocity, which mimics the flow pattern during walking, also increases the shearing forces on the endothelial cells resulting in several fold increase in the release of important bio-chemical mediators such as tissue plasminogen activator, tissue factor pathway inhibitor, nitric oxide, and prostacyclin, all serving as the bodies own anti-coagulant factors and therefore effecting it's hypercoagulability state.
Since increase peak venous velocity provides many benefits, it has become an objective of various conventional devices to create high peak venous velocities through mechanisms that will be well tolerated by the patients. As studies have shown, the velocity of venous flow is proportional to the pressure exerted on the limb and to the rate at which the pressure rises. Thus, systems have been developed to create relatively high pressures (70-130 mmHg) with relatively high rate of pressure rise (0.3-1 sec) in order to show improvements in flow outcome (peak venous velocity) over slower inflating devices.
Various conventional compression devices are known for applying compressive pressure to a patient's limb. These types of devices are used to assist in a large number of medical indications, mainly the prevention of deep vein thrombosis (DVT), vascular disorders, reduction of edemas, and the healing of wounds. Prior art devices are typically divided into two main segments: 1) a hospital segment, in which the conventional compression devices are used mainly for the prevention of DVT and 2) a home segment, in which the conventional compression devices are mainly used to treat severe lymphedema. Although showing high clinical efficacy in clinical studies in treating the above clinical indications, the conventional compression devices share many disadvantages that severely hamper their clinical out come in real life situations.
For example, the conventional compression devices use a conventional main power supply (wall outlet), and thus impose confinement upon the patient during the long periods of treatment e.g.: in DVT prevention after surgeries, the patients should be on therapy continuously from before the operation until discharge on a 24/7 basis. Confinement to the bed for receiving continuous treatment with a conventional device is impractical and is hardly ever achieved. Moreover the need to stay lying in bed for long periods of time delays recuperation, can lead to the development of pressure ulcers, and is contra-indicated to good medical practice.
The pump unit of the conventional compression device is heavy (5-15 pounds), which makes it hard to maneuver and place in the vicinity of the patients. The pump unit is also big and thus creates a storage problem, specifically in hospitals, in which tens and hundreds of units are stationed, usually in a special storage room. The sleeve of the conventional compression device is big and ungainly, and thus restricts the movement of the limb it encompasses and imposes discomfort. In addition, the use of multiple cells demands the use of multiple conduits (usually one for each cell) making the whole system more cumbersome and harder to maneuver.
Moreover, data corresponding to the pressure and compression cycles of the conventional compression systems has to be manually entered into the system by the clinical staff each time the system is turned ON. Furthermore, since the error detecting mechanism of the conventional systems shuts OFF the system each time an error is detected, the system needs to be manually restarted by the clinical staff, thereby requiring the clinical staff to manually re-enter the data corresponding to the pressure and compression cycles. In other words, in view of the need to manually enter the data corresponding to the pressure and compression cycles upon each start-up of the compression system and in view of the shutting down of the system upon error detection, with the accompanying re-entry of data, the conventional compression systems are overly dependent upon clinical staff for operation, thereby unduly imposing on the workload of the clinical staff.
All of the aforementioned disadvantages result in poor patient and therapist (mainly nurses) compliance and compliant. Clinical studies have proven that daily compliance of the systems is less then 50% resulting in far below expectation clinical outcomes compared to a continuous treatment (“Prophylaxis against DVT after Total Knee Arthroplasty,” by Geoffrey H. Westrich, The Journal of Bone and Joint Surgery, Vol. 78-A, June 1996 & “Why does Prophylaxis with External Pneumatic Compression for DVT fail?” by Anthony J. Comerota, The American Journal of Surgery, Vol. 164 September 1992).
As noted above, in many medical conditions it is desirable to apply pressure to a region of the body surface. Conventionally, this is accomplished by fixing one or more individually inflatable cells to the body surface. When the cells are inflated, a pressure is applied to the body surface in contact with the cell. When the cell is deflated, the pressure is relieved. The cells are usually incorporated into a sleeve that is placed around a body limb to be treated. The limb may be, for example, a leg, an arm, a hand, a foot, or the trunk.
The cells may be toroidal in shape when inflated so as to completely surround the limb. A cell may be maintained in an inflated state for a prolonged period of time in order to apply prolonged pressure to the underlying body region. Alternatively, a cell may be inflated and deflated periodically so as to apply intermittent pressure to the underlying body region. A sleeve having one or more individually inflatable cells will be referred to herein as a pressure sleeve.
FIG. 20 schematically shows a prior art system for applying pressure to a body limb. The system uses a pressure sleeve (not shown) comprising one or more individually inflatable cells. The system also includes a console 615 containing a compressor 602 that generates pressurized air. A conduit 607 conducts the flow of pressurized air away from the compressor 602. A number of solenoid valves (605a, 605b, and 605c) equal to the number of cells in the pressure sleeve are positioned along the conduit 607. Each valve (605a, 605b, and 605c) has an air inlet connected to an upstream portion of the conduit 607, a first air outlet connected to a downstream portion of the conduit 607, and a second air outlet (611a, 611b, and 611c) connected to an associated cell via a conduit (614a, 614b, and 614c). Each valve can alternate between an open state in which pressurized air can flow between the inlet and the first outlet and the second outlet (611a, 611b, and 611c) and a closed state in which pressurized air can flow between the inlet and the first outlet, but not between the inlet and the second outlet (611a, 611b, and 611c).
The console 615 further comprises a processor 619 that controls the state of each of the valves (605a, 605b, and 605c) so as to execute a predetermined temporo-spatial array of inflation of the cells. For example, in one application the cells are inflated peristaltically so that one cell is first inflated, while the other cells are deflated. As illustrated in FIG. 16, this can be accomplished by the processor 619 opening the valve 605a while the valves 605b and 605c are closed. Pressurized air flows in the conduit 607 from the compressor 602 into the cell associated with conduit 614a. The processor 619 monitors the air pressure in the conduit 607 by means of a pressure gauge 603. When the pressure has reached a predetermined level, the processor 619 closes the valve 605a. Next, the cell associated with conduit 614b is inflated by opening the valve 605b. A one-way valve 625 prevents the flow of air in the conduit 607 from flowing from the valves (605a, 605b, and 605c) towards the compressor 602. The cell associated with conduit 614a is then deflated and the cell associated with conduit 614c is inflated. The cells associated with conduit 614b and 614c are then deflated, and the cycle can begin again.
The console 615 has a housing 620 containing the processor 619, the conduit 607, and the valves (605a, 605b, and 605c). The compressor 602 may be located within the housing of the console 615 as shown in FIG. 20. In the conventional compression system, as shown in FIG. 20, pressure in the cells rises gradually, starting when the valve 605a is opened until the final pressure is achieved. However, in some medical conditions it is beneficial to produce a fast inflation of the sleeve encompassing the body surface. Studies have shown that the velocity of venous flow or the increase in local arterial flow is proportional to the rate at which the pressure rises. In the prevention of DVT, it is believed that this acceleration of venous flow reduces the risk of pooling and clotting of blood in the deep veins and therefore the rate of pressure rise is a critical variable of effectiveness in the prevention of DVT. In order to achieve a rapid inflation, it is known to incorporate in the housing 620 of the console 615 a pressure accumulator.
FIG. 21 shows schematically another conventional compression system for applying pressure to a body limb incorporating a pressure accumulator 740. This conventional compression system contains several components in common with the conventional compression system shown in FIG. 20. As illustrated in FIG. 21, a solenoid valve 705a is positioned on the conduit 707 upstream from the valves (705b, 705c, and 705d). The valve 705a has an air inlet connected to an upstream portion of the conduit 707, a first air outlet connected to a downstream portion of the conduit 707, and a second air outlet connected to the pressure accumulator 740 via a conduit. The valve 705a can realize an open state in which flow of fluid may occur between the inlet, the first outlet, and the second outlet. The valve 705a can also realize a closed state in which flow of fluid may occur between the inlet and the first outlet but not between the second outlet and the inlet or between the second outlet and the first outlet. The processor 719 determines the operational state of valve 705a. 
The conventional compression system shown in FIG. 21 is used when it is desired to apply pressure rapidly to a portion of a body limb underlying the cell. In this application, the valve 705a is opened while the valves (705b, 705c, and 705d) are closed, causing pressurized air to flow in the conduit 707 from the compressor 702 through the valve 705a into the accumulator 740. When the pressure in the accumulator 740 reaches a predetermined value PA, as determined by the pressure gauge 703, the processor 719 opens the valve 705b causing air to flow from the accumulator 740 into the cell associated with valve 705b. The pressure in the cell associated with valve 705b will rise rapidly to a pressure PC. PA and PC satisfy the relationship PAVA=PC(VA+VC) where VA is the volume of the accumulator 740 and VC is the volume of the cell associated with value 705b when inflated. The valves 705b, 705c, and 705d are then operated as described in reference to the system of FIG. 20.
Systems of the type shown in FIG. 21 having an accumulator inside the console are disclosed, for example, in U.S. Pat. Nos. 4,653,130 and 5,307,791 to Senoue et al.; U.S. Pat. No. 5,027,797 to Bullard; U.S. Pat. No. 5,840,049 to Tumey et al.; and U.S. Pat. No. 5,588,955, to Johnson et al. The entire contents of U.S. Pat. Nos. 4,653,130; 5,307,791; 5,027,797; 5,840,049; and 5,588,955 are herby incorporated by reference.
As illustrated in FIG. 21, the presence of the accumulator 740 within the housing 720 of the console 715 adds to the size of the console 715. Thus, adding an accumulator to the console of a system that is otherwise miniature, mobile and battery operated makes the console, and hence the entire system, immobile, which destroys the advantages and benefits of a mobile system.
All the above-described devices use a pump, a reservoir that receives pressurized air from the pump, an inflatable cuff for sequentially applying pressure to a limb, and means for intermittently and quickly transmitting pressurized air from the reservoir to the inflatable cuff. The triggering mechanism for the compression cycles used in these devices is a timer that is set to initiate the compression cycle every 30-50 seconds (depending on the specific system) with out taking into consideration the phasic nature of the venous flow in the recombine position. This phasic flow is created mainly by the changes in the intra-abdominal pressure that is caused by the respiration mechanism. During inspiration, the contraction of the diaphragm muscle causes an increase in the intra-abdominal pressure, and the contrary happens during expiration. Triggering the compression cycle regardless of the natural phasic venous flow creates non-consistent, non-reproducible peak venous velocities.
In other words, the effects of external compression being applied during expiration (when the intra-abdominal pressure is least) will be positively reinforced and/or enhanced by the lower intra-abdominal pressure, the lower pressure acting to draw the blood, thereby effectively increasing the potential peak venous velocity. On the other hand, the effects of external compression being applied during inspiration (when the intra-abdominal pressure is greatest) will be adversely impacted and/or diminished by the higher intra-abdominal pressure, the higher intra-abdominal pressure acting to block or pushback the blood flow, thereby effectively lowering the potential peak venous velocity and compromising the efficacy of the device. Moreover, it is now understood that the increase of the peak venous velocity by the external compression is dependent on the exact point in the phasic flow in which the external pressure was administrated. Since conventional devices use timers as the triggering mechanism, the measured peak venous velocities for these devices vary tremendously.
In summary, the external compression generated venous flow being in-phase with the phasic nature of the venous flow creates a positive synergistic effect and a high peak venous velocity, whereas external compression generated venous flow being out of phase with the phasic nature of the venous flow is subjected to negative interference from the phasic nature of the venous flow.
Therefore, it is desirable to provide a compression system that provides external compression generated venous flow in synergistic synchronization with the phasic nature of the venous flow. More specifically, it is desirable to provide a compression system that provides external compression generated venous flow during times of lower intra-abdominal pressure. Furthermore, it is desirable to provide a compression system that provides external compression generated venous flow in synergistic synchronization with the respiration cycle of the patient. In addition, it is desirable to provide a compression system that is small, ambulant, and portable. It is also desirable to provide a compression system that provides patients with continuous 24/7 treatments and freedom of movement. It is further desirable to provide a compression system that is suitable for home use and can be stored easily and/or allows a user to engage in social activities during treatment. Lastly, it is desirable to provide a compression system that includes a pressure accumulator that is small, ambulant, and portable.